1. Field of the Invention
The present invention relates to the transfer of workpieces such as semiconductor wafers within a storage and transport pod, and in particular to a latch locking mechanism preventing unwanted opening of the pod.
2. Description of Related Art
A standardized mechanical interface system (SMIF) proposed by the Hewlett-Packard Company is disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of a SMIF system is to reduce particle fluxes onto semiconductor wafers during storage and transport of the wafers through the semiconductor fabrication process. This purpose is accomplished, in part, by mechanically ensuring that during storage and transport, the gaseous media (such as air or nitrogen) surrounding the wafers is essentially stationary relative to the wafers, and by ensuring that particles from the ambient environment do not enter the immediate wafer environment.
A SMIF system has three main components: (1) minimum volume, sealed pods used for storing and transporting wafers and/or wafer cassettes; (2) an input/output (I/O) minienvironment located on a semiconductor processing tool to provide a miniature clean space (upon being filled with clean air) in which exposed wafers and/or wafer cassettes may be transferred to and from the interior of the processing tool; and (3) an interface for transferring the wafers and/or wafer cassettes between the SMIF pods and the SMIF minienvironment without exposure of the wafers or cassettes to particulates. Further details of one proposed SMIF system are described in the paper entitled xe2x80x9cSMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURING,xe2x80x9d by Mihir Parikh and Ulrich Kaempf, Solid State Technology, July 1984, pp. 111-115.
Systems of the above type are concerned with particle sizes which range from below 0.02 microns (xcexcm) to above 200 xcexcm. Particles with these sizes can be very damaging in semiconductor processing because of the small geometries employed in fabricating semiconductor devices. Typical advanced semiconductor processes today employ geometries which are one-half xcexcm and under. Unwanted contamination particles which have geometries measuring greater than 0.1 xcexcm substantially interfere with 1 xcexcm geometry semiconductor devices. The trend, of course, is to have smaller and smaller semiconductor processing geometries which today in research and development labs approach 0.1 xcexcm and below. In the future, geometries will become smaller and smaller and hence smaller and smaller contamination particles and molecular contaminants become of interest.
SMIF pods are in general comprised of a pod door which mates with a pod shell to provide a sealed environment in which wafers may be stored and transferred. So called xe2x80x9cbottom openingxe2x80x9d pods are known, where the pod door is horizontally provided at the bottom of the pod, and the wafers are supported in a cassette which is in turn supported on the pod door. It is also known to provide xe2x80x9cfront openingxe2x80x9d pods, in which the pod door is located in a vertical plane, and the wafers are supported either in a cassette mounted within the pod shell, or to shelves mounted directly in the pod shell itself.
In order to transfer wafers between a SMIF pod and a process tool in a bottom opening system, a pod is typically loaded either manually or automatedly onto a load port on a front of the tool so that the pod door lies adjacent the port door of the process tool. Thereafter, mechanisms within the load port decouple the pod door from the pod shell and lower the pod door and port door together into the minienvironment, with a wafer carrying cassette remaining seated on the pod door. The pod shell remains in position against the interface port to maintain a seal at the port and to define a sealed, clean environment including the interior of the process tool and pod shell. A wafer handling robot within the process tool may thereafter access particular wafers supported in the pod shell for transfer between the pod and the process tool.
During wafer storage and transport, the pod door is typically held affixed to the pod shell by one of two different latch assemblies. In a first system, referred to herein as a perimeter latch assembly, four independently operated latches are mounted to a bottom perimeter of the pod shell, with an engagement portion of each latch extending inward under the pod door to maintain the pod door in a sealed position in the pod. When it is desired to separate the pod door from the pod shell, each of the four latches is actuated outwardly, to withdraw each engagement portion from under the pod door, at which time the pod door may be separated. Each of the latches needs to be actuated outward to disengage the pod door from the pod shell. In conventional perimeter latch systems, the latches may be disengaged manually, or the pod may be seated on a load port or other support surface including four actuation pins. The pins fit into slots formed on each of the latches, and, after the pod is properly positioned on the support surface, the actuation pins move the each of the latches outward to withdraw the engagement portion of each latch from under the pod door. Thereafter, the pod door may be separated from the pod shell.
A single latch of a perimeter latch lock assembly is shown in prior art FIG. 1. As explained above, a latch 20 is mounted on the lower perimeter of pod shell 22, and includes an engagement portion 24 extending under the pod door 26. The latch 20 may be actuated either manually or by means of a pin (not shown) on a support surface engaged within slot 28 so as to move to the left from the perspective of FIG. 1. Once the latch 20 is moved sufficiently so that engagement portion 24 is clear of the pod door (and the other latches are similarly actuated, the pod door may be separated from the pod shell. The latch may be biased into sealing position shown in FIG. 1 by a spring or other biasing scheme, such as leaf spring 30 shown in FIG. 1.
A second type of latch assembly (not shown) is disclosed in U.S. Pat. No. 4,995,430, entitled xe2x80x9cSealable Transportable Container Having Improved Latch Mechanismxe2x80x9d, to Bonora et al., which patent is owned by the assignee of the present application. The mechanism disclosed therein includes a latch hub centrally mounted within the pod door, which latch hub engages with first and second translating latch plates. The latch plates include ends which extend beyond the footprint of the pod door and into slots in the pod shell. When the latch plates are in an extended position, the ends fit into the slots in the pod shell to seal the pod. When the latch plates are in a retracted position, the ends of the latch plates withdraw into the footprint of the pod door to allow separation of the pod door from the pod shell. When a pod including this type of latch assembly is mounted on a load port or other such support surface, mechanisms within the support surface rotate the hub to move the latch plates between their extended and retracted positions.
In the perimeter latch assembly, it can happen that an operator manually disengages each of the latches to open the pod when in fact the pod should not be opened. Such unwanted pod openings can lead to contamination of the workpieces within the pod and/or an improper exchange of one workpiece lot for another within the pod.
The present invention includes a latch mechanism for latching a first member to a second member, such as a pod door to a pod shell in a semiconductor environment. The latch mechanism includes a latch lock mounted to the first member, comprising a finger portion and an angled portion. A latch is mounted to the first member, adapted to move between a latched position and an unlatched position. The latch has an engagement portion that contacts a portion of the second member when the latch is in the latched position, so as to maintain contact between the first and second members. The latch also has a slot for receiving the finger of the latch lock. An actuation pin is positioned in the slot of the latch. The actuation pin is adapted move laterally between a first position and a second position. The actuation pin slidably contacts the angled portion, such that when the actuation pin moves between the first position and the second position the angled portion moves in a direction orthogonal to the lateral movement. This allows the finger portion to move into and out of the slot. The latch may then be moved between the latched and unlatched positions when the finger portion is not positioned in the slot.